Al-H and Al-D complexes in Si: A uniaxial-stress study of the hydrogen vibrational modes

Reorientation kinetics of hydroxyl groups in anatase TiO2

The reorientation kinetics of hydrogen in a variety of complexes in the anatase polymorph of TiO₂ was investigated by means of stress-induced dichroism. For the hydrogen-defect resulting in an O-H vibrational mode with a frequency of 3389 cm^-1, the energy barrier separating adjacent equivalent in-plane sites of hydrogen was determined to be independent of the isotope and equal to 0.74 ± 0.02 eV, whereas the attempt frequency was found to be (1.10 ± 0.20) × 10¹² and (0.75 ± 0.15) × 10¹² s^-1 for hydrogen and deuterium, respectively. The defect with vibrational modes at 3412 and 3417 cm^-1 previously assigned to isolated hydrogen did not reveal alignment under the stress up to room temperature, which indicates that the barrier of hydrogen motion is above 0.9 eV.

Hydrogen motion in rutile TiO2

Uniaxial-stress experiments have been performed for the 3287- and 2445-cm-1 local vibrational modes assigned to the positive charge state of interstitial hydrogen [Formula: see text] and deuterium [Formula: see text], respectively, occurring in mono-crystalline rutile TiO2. The onset of the defect alignment under the stress applied perpendicular to the [001] axis is detected at 165 K (185 K), which corresponds to the activation energy of 0.53 eV (0.58 eV) for interstitial hydrogen (deuterium). Based on these findings the diffusion constants of [Formula: see text] and [Formula: see text] along the [001] axis of TiO2 are determined. The experimental data are complemented by density-functional theory calculations and compared with the earlier results on the diffusion of [Formula: see text]/[Formula: see text] at elevated temperatures up to 700 °C. It is found that the activation energy value deduced from our low-temperature stress measurements yields a very good agreement with the high-temperature data, covering a dynamic range of 12 orders of magnitude.